Electronic equipment employing digital techniques, such as computing devices, and other electronic or electrical equipment, such as switching power supplies, cause electromagnetic interference (EMI) which can both be radiated and conducted. Designers and users of such equipment must be concerned with suppression of conducted EMI or noise because the noise can interfere with proper operation of other equipment which could be necessary to health and safety. Furthermore the U.S. Federal Communications Commission (FCC) and others have established regulations and standards regarding EMI emissions.
It is known to place a power line interference filter between the power source and the equipment causing the EMI. One such filter which has been used on power systems includes a plurality of generally cylindrical capacitors arranged in a generally rectangular array. Several ferrite inductive cores are mounted on one side of the array and feed through bus bars are passed through these inductors. Capacitor bus bars are connected to terminals at one end of each capacitor and are typically brazed to the feed through conductors. Terminals extending from the other ends of the capacitors are shorted by a shorting plate.
Another such filter is shown in U.S. Pat. No. 4,737,745 which describes an electromagnetic interference filter assembly having a pair of magnetic cores each having a central opening. The cores are mounted with their openings aligned along a common axis and feed through conductors pass through the openings. Two arrays of capacitors are mounted on opposite sides of the cores and capacitor bus bars serve to electrically connect corresponding ones of these capacitors in each array. A portion of each capacitor bus bar includes an aperture which is aligned along the common axis and through bolts which lie along the common axis which are used to hold the feed through conductors and capacitor bus bars in electrical contact with each other.
In many known filters, the magnetic cores and other electronic components are maintained in position by a potting material. This makes the precise positioning of the components difficult as the potting material is first introduced to the assembly as a liquid and must harden. Consequently, additional mechanical devices must be employed during manufacture to maintain the positioning of the components as the potting material solidifies. In addition, as the potting material solidifies, stresses may be introduced to the magnetic cores, causing magnetostriction, thereby reducing the effectiveness of the filter.
Although such known filter assemblies generally perform their intended function, it is desirable to provide an EMI filter assembly in which the electrical components are precisely located and stresses on the electrical components are reduced or controlled. In addition, it is desirable to provide filters which are smaller in size and which are easier to assemble than the filters known in the art.